10 Doctor Who Characters Who Can Never Die

Sam Swift and Ashildr are something of a package deal. When the Twelfth Doctor used that Mire repair kit to bring her back to life, he knew that he'd made Ashildr immortal - but not just that, he knew that he'd doomed her to a life of loneliness.

"Immortality is everybody else dying" he tells Clara, before adding that Ashildr might one day meet someone she can't bear to lose.

Fortunately then, the Doctor left her an extra repair kit, and this is where the wisecracking Mr. Swift comes in. Though he certainly wouldn't have been Ashildr's first choice, she used the repair kit on him to reverse his death, which was necessary to prevent the invasion of those aforementioned lion people. And with that repair kit being identical to the one the Doctor used on Ashildr, it stands to reason that Swift would also gain the gift of eternal life. Right?

Well, the thing is, we don't really know. At the end of the episode, the Doctor admits that he doesn't know what's going to happen to Swift, leaving Ashildr with the rather confusing comment "He might be around for a while. Or not. Who can say?"

Thanks Doctor, that really clears things up!